Rhizocarpon ridescens (Nyl.) Zahlbr.

A well distinguishable Rhizocarpon with a black prothallus, more or less scattered, bright yellow, strongly convex areoles, a part of which forms capitate soralia on the top. Apothecia are rare. In addition to rhizocarpic acid, it also contains psoromic or barbatic acid. The barbatic acid chemotype is sometimes recognized as a separate species R. sorediosum (e.g., Wirth et al. 2013, Nimis et al. 2018). Recently, two records from the Czech Republic were published under that name (Šoun et al. 2015, Malíček & Vondrák 2016). The richest known Czech population is at the Tisovec hill in the Krušné hory Mts, where it was also first recorded in the country (Bayerová et al. 2004), with both chemotypes present.

Generally, it is a rare Eurasian taxon. In the Czech Republic, it is currently only known from five localities, in western and central Bohemia. It grows on siliceous rocks rich in metals from the lowlands to the upper treeline. It prefers exposed natural rocky outcrops or also anthropogenic stands (e.g., spoil heaps).

Literature: Bayerová Š., Halda J., Liška J. & Uhlík P. (2004): Rhizocarpon ridescens a Verrucaria ochrostoma ‒ dva nové druhy lišejníků pro Českou republiku. ‒ Bryonora 33: 26‒27. Wirth V., Hauck M. & Schultz M. (2013): Die Flechten Deutschlands. – Ulmer, Stuttgart. Šoun J., Bouda F., Kocourková J., Malíček J., Peksa O., Svoboda D., Uhlík P. & Vondrák J. (2015): Lišejníky zaznamenané během jarního setkání Bryologicko-lichenologické sekce ČBS na Manětínsku (západní Čechy) v dubnu 2014. ‒ Bryonora 55: 20‒36. Malíček J. & Vondrák J. (2016): Zajímavé nálezy lišejníků ve středním Povltaví II. – saxikolní druhy. – Bryonora 58: 46–65. Nimis P. L., Hafellner J., Roux C., Clerc P., Mayrhofer H., Martellos S. & Bilovitz P. O. (2018): The lichens of the Alps – an annotated checklist. – Mycokeys 31: 1–634.

Ascomycota → Lecanoromycetes → Rhizocarpales → Rhizocarpaceae → Rhizocarpon